But after making some lifestyle changes at the beginning of this year, the dancing pro has lost about 15 lbs. – and poses in a bikini as part of PEOPLE's Most Talked About Bodies special issue.

"My waist is cinched and I can see an outline of my abs!" says Burke, 30, who now weighs 120 lbs.

During any given season of the reality ballroom competition, "I always lose weight – around 5 to 7 lbs.," she explains. "It's because of our strenuous rehearsals and long hours, which is not relatable to anybody because you're working out 8 to 10 hours a day.”

But instead of just falling into a funk between seasons, Burke headed to Hawaii with her family last December and "I made sure I worked out," she says. "I wanted to eat what I wanted but I made sure that portion control was basically half of what I normally would eat."

Aside from her grueling rehearsal routine, Burke found that friendship was a great exercise motivator for the past few months: During last season, she befriended contestant Leah Remini.

"We really bonded," Burke says. "She lives down the street from me so we're able to get up in the morning and work out together. When you have a buddy to work out with, you don't want to flake on that person."

She also credits trainer Brendan Johnston for motivating them both with a circuit-training regimen when she's not dancing.

"We'll run a mile on the treadmill, then get off and do biceps, triceps, squats, and repeat that about three times," she explains. "Then we'll do abs towards the end. It shocks your body more than if you were just on a treadmill for three miles."

When it comes to sustaining her healthy lifestyle, Burke is willing to work: "When I started the show 10 years ago, my metabolism was obviously different because I was 20!" she says. "Turning 30, you see changes. You have to work harder as you get older."

To read more on Cheryl's daily diet and what other stars eat in a day, pick up the new issue of PEOPLE on newsstands Friday.